1. Field of the Invention
This invention relates to plate and fin type heat exchangers, and particularly to a heat exchanger core of controlled resistance to heat flow.
2. Description of the Prior Art
In the heat transfer arts, a known type of heat exchanger core is comprised of stacked plate elements and spacer elements forming a layered device in which fluids of different temperatures flow through adjacent layers. A transfer of heat occurs, through intervening plates, from the fluid of higher temperature to the fluid of lower temperature. Core parts are conventionally made of lightweight metals of good heat conductivity adaptable to being joined to one another by a brazing process. Plate elements are made as thin as structural considerations permit. Corrugated fin material between plate elements supports the plate elements and provides secondary heat transfer surface. Heat transfer between liquids, between gases and between liquids and gases commonly is undertaken in such core devices.
The so-called plate and fin type heat exchanger is and has been in general use, its construction having become largely standardized. Its use has not been obvious, however, in application of severe requirements, particularly when those requirements are involved in system operations. In one such application, a fluid normally in gaseous form (at other than very low temperatures) is pre-cooled to a liquid form. In that form is is pumped to and through a heat exchanger where it is in heat transfer relation to another fluid of substantially higher temperature. In its passage through the heat exchanger the liquid is highly volatile. Rapid vaporization can induce pressure pulsations which, as reflected in the system of which the heat exchanger is a part, can have undesired consequences. Desirably, vaporization should proceed at a controlled rate and not in a burst of activity in early portions of the liquid flow paths. In attempting to cope with this problem it has been variously suggested that parts of the heat exchanger core should be made relatively heavy or should be made of different metals, or that dimensions of the core be substantially changed from those given heat transfer specifications may require. Disadvantages inhere in all such proposals, not the least of which is that all necessitate a use of non-standard parts and special fabrication.
I am not aware of other proposed solutions to the described problem. I am aware of the teachings in Parker U.S. Pat. No. 3,880,232 and Parker U.S. Pat. No. 4,049,051. These relate to a different problem in that they attempt to avoid core splitting and cracking in a gas to gas heat exchanger. Moreover one suggests a use of combinations of metals and the other suggests progressive zoning in existing flow paths to improve thermal fatigue life.